Among the raft of changes to the planning rules announced by the government is a temporary relaxation of laws surrounding domestic extensions in England. The full detail will be in a consultation document, expected to be published next week, but here we look at the current rules and how they might change.

What can I currently build?

You can apply for planning permission to build anything you like, although it may very well not be granted, or if you want to make more minor changes without planning permission you can opt for a permitted development. It is the rules around what this constitutes which the government wants to relax.

What currently counts as a permitted development?

It depends where you live: conservation areas and listed buildings have different rules, but broadly speaking extensions, loft conversions and conservatories can all be permitted developments. There are, however, restrictions. When it comes to extensions the main ones are:

• all extensions and other buildings must not exceed 50% of the total area around the house as it stood on 1 July 1948, or the day it was built if later.

• the extension is not on the side of the house that faces the road.

• on a detached house a single storey extension can be up to 4m long and side extensions can only be a single storey.

• on a terraced or semi-detached house a single storey extension can only be 3m long.

• the building must not be clad in any outlandish material – if you want to do something that doesn't match the exterior of your house you will need to get the council's permission.

What about my loft?

You can do a lot to a loft without planning permission – most conversions are permitted developments. However, you will need permission if you want to add a dormer to the front of a house or raise the roof level in any way. You will also be restricted to creating space equal to 40 cubic metres in a terraced house and 50 cubic metres in a semi-detached property.

How will this change under the government's proposals?

It is unclear if there will be any change to the rules surrounding loft conversions. The proposals are expected to include new rules on single storey extensions, which will double the length of a permitted development. This will mean:

• on a detached house a single storey extension can be up to 8m long.

• on a terraced or semi-detached house a single storey extension can be 6m long.

Rules on height, materials and so on are expected to remain unchanged.

Great, anything I need to know before I start building?

Only that the rules are not quite as hard-and-fast as they sound. Chris Wojtulewski, director of planning consultancy Parker Dann, says the rules around permitted developments are "intensely complicated" and councils have a 49-page guide to applying them. "There are subtle variations between local authorities – inevitably people are going to have different interpretations of the rules."

Wojtulewski suggests homeowners who are in any doubt about whether their proposed build is or isn't permitted should contact their local council for clarification at the beginning of the process.

You also need to be aware of building regulations: if an extension doesn't meet them a council can ask for it to be taken down. If you are employing a builder to do your work make sure you confirm they are taking responsibility for meeting the rules.

Can my neighbours complain?

When a homeowner applies for planning permission the council sends out letters to neighbours asking if they have any objections. These are taken into account when a planning officer makes a decision, although the fact a neighbour has complained does not necessarily mean a scheme will be rejected.

This process doesn't occur if you are building a permitted development, but you will still need to notify your next-door neighbours if you are building near to your boundary. Once you start building, any neighbour who believes you are breaking the permitted development rules can contact the council, which will send round an enforcement officer.

When will the new rules apply?

The government is putting the proposals out to a month-long consultation, with a view to changing the rules before the end of the year. They will be in place until the end of 2015.

Is this going to kickstart the economy?

It seems unlikely, and the effects of the changes will be difficult to quantify. Annually there are 400,000 planning applications processed, with almost 200,000 for residential improvements, many of which are for changes such as conservatories or extensions.

Councils do not publish figures for how many of these are rejected, and some householders who are turned down will have gone through with smaller extensions under existing permitted development rules, so it is impossible to say how much extra building work will be done in the nation's back gardens.

Jonathan Harris, director of mortgage broker Anderson Harris, says planning isn't the issue holding many homeowners back. "It's all well and good suggesting the answer to the housing crisis is to extend existing properties, but unless you have got the £20,000 upwards to pay for it sitting in your bank account, there could be funding issues.

"Lending is tougher than before the downturn so getting your mortgage lender to advance the required funds will not be as easy as in the past."